Abrasive sheet material



Sept 5, 1944 J. H. KUGLER ET Al.

BRASIVE SHEET MATERIAL Filed Oct. 29, r1938 SSG wl.,

uw. "RM1 Patented Sept. 5, v1944 ABRASIVE SHEET MATERIAL Joseph H. Kugler and Byron J. Oakes, St. Paul,

Minn., assignors to Minnesota Mining & Manufacturing Company, St. Paul, Minn., a. corporation oi' Delaware Application October 29, 1938, Serial No. 237,760

Claims.

The present invention relates to new articles of manufacture and to method of producing the same. It involves an article in which two or more coatings or layers of material are joined in adhering or contiguous relation.

stretch out or otherwise undergo change from its original dimensions, for example, due to fluids encountered during use or because of poor adhesion between the binder coat and impregnated While the invention has other embodiments, l

as will be understood from the application taken as a whole, one important adaptation is a sheet abrasive article in which a grit-bonding or binder coat is joined in integral and contiguous relation with a backing coat. Where the sheet abrasive article includes a iibrous material, e. g., 'a fabric backing, one coat may serve to impregnate the fibrous or like material and then the binder or grit-bonding coat may be adjacent to and joined in integral relation with the impregnated fibrous backing.

This invention is, in certain aspects thereof, an improvement over or further development of copending application Serial No. 558,872, filed on or about August 24, 1931'.

It is an object of this invention to produce 'an layers of material which are joined together with a strong bond. 'A still further object is to improve the bond between'a fibrous sheet land a gritbonding or other coating, as the case may be, by first giving the fibrous sheet an impregnating treatment or applying thereto a backing coat of a different material. Another object is to provide abrasive belts and like articles of improved quality. These and other objects and advantages` will appear from the application as a whole.

Illustrative of articles within the scope of this invention are abrasive belts of an improved type and construction. Abrasive belts known to me, which were in use prior to this invention, had various defects. When some of them were exposed to conditions encountered during use, the grit-bonding or binder coat would loosen from or shell oli of the brous backing. This condition might be due to poor adhesion between the binder coat and the backing and/or to a tendency of the fibrous backing to become raggy and to fibrous backing in the first instance. Various other defects existed in abrasive belts heretofore employed, which it is an object of this invention to overcome.

For the sake of illustrating our present invention, and not limiting it, reference is made to the appended drawing, in which:

Figure 1 is an enlarged diagrammatic illustration in section of a piece of untreated cloth backing.

Figure 2 is an enlarged diagrammatic illustrabacking.

Figure 3 is an enlarged diagrammatic illustration in section of a finished abrasive belt.

Figure 4 shows, diagrammatically, an example oi a belt made according to the present invention and how it may be used in a sanding machine.

Figure 3 shows the cloth backing i0 impregnatedv by treatment with an impregnating or presizing coat il. To this impregnated cloth the binder or grit-bonding coat l2 is applied. The abrasive grits i3 are shown embedded in this binder coat l2 and the sandsize coat it is shown overlying the binder coat l2, between the grits` i3.

In Figure 4 the completed belt i5 is shown with the abrasive coating on its outward side. Belts made according to our invention may be used in a wide variety of machines that are designed to abrade with abrasive belts. For the sake of clarity and to provide a convenient means of illustrating a completed belt in a drawing, the belt in Figure 4 is shown mounted in a sanding machine that supports the belt by two pulleys which contact the belt on its non-abrasive or inward side. The article i6 which is to be abraded by the belt, and which is illustrated as a sheet of glass being edged or smoothed, is pressed against the moving belt at the point at which the belt is backed up by the shoe il.

It is to be understood that the drawing is simply illustrative of one specific embodiment of the present invention, and is in no sense intended as a limitation.

In the making oi abrasive belts, according to a Apreferred aspect of this invention, the woven fabric or other fibrous material may be coated on either or both sides, as by immersion, or otherwise coated or impregnated with a thermoplastic and/or polymeric or resinous material of the type herein illustrated which, in its solidiiied condition, is of good or sufficient elasticity, Thermoplastic materials which contain natural or synthetic polymers and which are not brittle under ordinary temperatures of use are especially contemplated. Illustrative of this class of materials are: polymerization products of ethylene linkage compounds (though the polymers themselves crdinarily contain no ethylene linkages). and of certain other multi-bond carbon to carbon linkage compounds, for example various polymeric vinyl compounds of the water-proof or waterdispersible types; cellulose derivatives which are thermoplastic and will provide a good bond between the grit-binder coat and the fibrous backing, such as various esters and ethers of cellulose, for example, ethyl cellulose: and substituted butadiene polymers such as chiot-butadiene or methyl butadiene. Materials of the types indicated above may be used alone as a backing treatment or impregnating coat for fibrous belts or the like or may be employed in admixtures. Admixtures containing materials of each of the above types have been employed and also admix- 'tures oi' materials of the above types with other materials not thus far mentioned, including other resinous or polymeric materials and/or solvents, plasticizers, modifiers and stabilizers, have been used for the purposes indicated.

Where materials of the above type are used as a backing coat or as an. impregnating coat, a phenolic resin such as a condensation product of phenol and formaldehyde, or cresol (or other substituted phenolic material) and an aldehyde, or alkyd modifications of phenol-aldehydes may be used to advantage as the grit-bonding or binder coat, although other materials such as alkyds, urea-aldehydes, etc., may be used in above example, in addition to litharge, lead stearate, lead oleate, calcium stearate, slaked lime or, for example, one of the common lead pigments such as lead oxide or lead carbonate may be used, and is `often milled into the vinyl resin solvent mixture, as by the use of a paint combination with or in lieu of phenol-aldehyde Y resins.

TheJ invention will be further illustrated by the following specific compositions adapted for use as an impregnating or backing coat or sizing for fibrous materials, e. g., for woven backing materials such as commercial drills" or other suitably 4woven fabric, such as "jeans," where cloth backing is employed. Drills or other fabrics, woven so as to reduce stretching thereof to a minimum, are especially desirable in making abrasive belts.

Example 1 Parts by weight Vinyl acetal resin 14 Litharge 27 Methyl-amyl ketone (solvent) 42 Carbon black 2 In place of the vinyl resin given in the example above, certain| other polymeric or resinous compounds may be used; also the litharge and solvent mentioned are not essential ingredients. For example, certain other vinyl plastics, including polyvinyl alcohol (treated if desired, byY

chemical or physical agents to render it insoluble), other vinyl acetals (e. g.. reaction products of polyvinyl alcohol and one or more of mill. In general, various materials which will serve the function of a stabilizer, i. e., will serve to neutralize any slight acidity which may develop from certain vinylites, may be employed for this purpose.

In place of the specic solvent above mentioned, various other ketones, for example, ketones such as methylethyl ketone, or higher ketones, or the like, may be employed, as well as various other solvents. Other solvents or diluents, such as the so-called coal tar solvents, including benzols, and the like, may, if desired, be employed in combination with ketones, for example to reduce the cost of solvent used in the coating or impregnating operation.

A preferred method of making abrasive belts, using the above composition or its equivalent, is to saturate completely the cloth backing, for example by causing the belt of cloth to run through a bath of the composition of Example l while the latter is maintained at temperatures of the order of room temperatures or F. Though these temperatures are not essential, a. temperature slightly above room temperatures promotes fluidity of the bath but, if temperatures are increased too much, undue volatilization of the solvent will occur. The cloth belt, after having been saturated, is allowed to stand on racks, usually at temperatures sufficient to promote the desired rapidity of volatllization of the solvent but not so high asto cause blistering or bubble formation. Room temperatures' and slightly higher temperatures, e. g., 100 F. or so, though not essential, have been employed with satisfactory results during the initial stages of the drying operation. After a good deal of the solvent yhas been evaporated (where a solvent is used), higher temperatures,'e. g., 175 F., are satisfactory and, in the interest of conserving time. are definitely advantageo-us. After the solvent has been largely evaporated, then the belt may be calendered. This is a type of ironing process and may be carried out by passing the belt or web between rolls which run at different speeds, thus maintaining the web of impregnated or coated fabric under tension. This may be accomplished by feeding the web or belt under tension to a standard three-roll calender and withdrawing thel web from the calender under tension. This operation sets the stretch in the fabric and both flattens down the Weave of the cloth as well as any lint or fuss on the surface thereof, thus providing a smooth surface.

Next aback-size coat may be applied to the belt, and then a presize coat. One material which may be employed with good results for one or both of these coatings is a phenol-aldehyde resin. However, in many cases, an abrasive fabric or belt of improved quality will result where, instead oi' using phenol-aldehyde resins, a vinyl resin or an ethyl cellulose resin, or materials of that type, or mixtures containing the same, are employed as a presize and/or as a back-size coat instead of phenolic resins. The belt is then cured. Where the presize and backsize coats comprise phenolaldehyde resins, the curing may be carried out by subjecting the belt to temperatures, for example, of the order of F. to 175 F. for two or three hours, thus only partially to set the phenol-aldehyde resin. Where different materials are employed. for the presiize and/or the back-size coat, colnditions suitable for the curing of these materials should be chosen as the circumstances require. Next the grit-bondingr or binder coat may be applied. For many uses, the grit-bonding or binder coat advantageously contains or comprises a phenolaldehyde resin or a modiiied phenol-aldehyde resin, e. g. an alkydI modified phenolic resin or non-thermoplastic, heat-convertible alkyd or urea-aldehyde resins or other material of generally similar characteristics.

At the time of the application of the binder coat to be impregnated or coated webor fabric, or just shortly thereafter, the granular material or abrasive particles may be applied so that the same become embedded in the binder coat while the latter is in a mobile or plastic condition. Now the belt is again cured, a't temperatures like those mentioned above or at higher temperatures, e. g., up to temperatures of the order of 200 F., for five or six hours, more or less.

Next an abrasive sizing or sand-size coat may be applied. This is normally of a character similar to the grit-bonding or binder coat and may be identicall therewith. For example, it may be a phenol-aldehyde resin or other like resins,

which ordinarily are at least as hard as the gritbonding coat.

Next the coated fabric may be cut into desired sizes and shapes and then cured at elevated temperatures of the order of 130 to 160 C. (266 to 320 E).

Other compositions which may be used as imprefznating or sizing,Y or backing coats follow.

Certain materials. of which that of Example 3, infra, is an illustration, are not ordinarily ap plied to fabrics in the manner in which vinyl resins may be employed. The usual practice is to soften such compositions, usually on a rubber mill, and then friction it into the cloth or fabric on calender rolls` which at one and the same time stretch the fabric longitudinally and iron down the fibers thereof while coating or impregnatim7 the fabric with a composition such Example 3 Parts by Weight.

2'chlorl,3 butadiene (e. g., neoprene) 100 Extra light calcined magnesia 10 Rosin oil (softener) 5 Brown factice 20 Carbon black 100 4Q Phenyl beta naphthylamine 2 Flowers of sulphur 1 Zinc oxide 10 type of composition and coating operation sets v the stretch of the fabric very satisfactorily.

Where a bonding or abrasive-binder coat of the` may then be applied to the composite abrasive article and the latter subiected to curing temperatures of the order of 150n F. to 300 F. without decomposing or embrittling the thermoplastic composition or' appreciably deteriorating the fabric. However. temperatures above about' 325 or 350 F. are preferably avoided in many if not most instances.

Where grit-bonding coats are employed which will adhere more firmly to a fabric covered with the composition as illustrated in Example 3. infra, rather than to a starved side of the fabric, it willfbe understood that the above fabric may be thoroughly impregnated with the above composition or that such composition may be applied to both sides of the fabric in the manner above described or in any other suitable manner.

While insolubilized glue, etc., arev mentioned above as a possible grit-bonding coat, it will, of course, be understood that phenol-aldehyde resins and other materials mentioned hereinabove are contemplated for this purpose where a composition as given in Example 3 is employed as ranuimpregnating or backing coat.

Example 2 Parts by weight Ethyl cellulose 20 20% ethyl alcohol plus 80% toluol (solvent) 80 hydrocarbons, etc., being employed as a solvent for the ethyl cellulose. In place of ethyl cellulose, cellulose acetate has been employed with good results; also many other esters and ethers.

of cellulose and certain other cellulosic derivatives, such as benzyl cellulose, may be employed.

The butadiene polymer of the above example may be employed with or replaced by other' substituted butadiene polymers, for example methylbutadiene. and/or dimethylbutadiene. This material may be applied to fabrics substantially in the manner already described hereinabove, preceding Example 2. However, where desired` this material may be employed in the form of a solution or emulsion.

The composition of Example 3 can be milled (e. g., on a rubber mill) and can be applied to a fibrous backing by frictioning the same into the fiber, that is, it illustrates a suitable material of a rubbery nature. such compositions are customarily loaded with various materials, e. g., with carbon black, zinc oxide, or other materials or pigments, for various reasons, one being to increase their strength.

'I'he elements of the composition given in .Evample 3, it will be understood, are illustrative only. In addition io the variations or changes in the butadiene polymer, which are above suggested, the rosin oil may be replaced by other softeners of an oleaginous or non-oleaginous nature, e. g., rosin, hydrocarbon oils, stearic acid, etc. The magnesia may be replaced by other materials which will accelerate the vulcanization and counteract acids which may form, e. g., other alkaline earth or alkali oxides or carbonates, etc. Carbon black may be replaced by other materials which will give added strength, will opacify the rubbery mass and/or Friction stocks from v serve as a filler. A function of the sulphur is to accelerate the vulcanization ofthe butadiene, etc., while the phenyl beta naphthylamine acts as an anti-oxidant (and to. some extent as an accelerator). The zinc oxide also acts somewhat as an accelerator but perhaps primarily as a filler. It will be obvious that flowers of sulphur and accelerators such as those specilically mentioned may be replaced by substitute if not equivalent agents. v The brown factice may bereplacedby white factice or various modified or vulcanized vegetable oils which will lserve the functions oi' brown factice, including aiding in arriving at a smooth spreading coating.

In making articles such as abrasive belts, which are often subjected to rough usage and severe stresses, there are relatively few materials, known as of the filing date hereof, which can be satisfactorily employed in impregnating the -cloth or fibrous backing material. Vinyl resins, such as those hereinabove set forth, are excellent materials for this purpose, particularly when a coating of a phenol-aldehyde resin or a modified phenolic aldehyde resin is applied in contiguous relation with the polymeric vinyl compound or with the fabric impregnated therewith. This situation-exists where the fabric is impregnated or saturated with a vinyl resin and then is given a presize coating of the same or another vinyl resin, the phenol-aldehyde condensation product vinyl chloride is not at all indispensable and e vinyl resins containing no polyvinyl chloride are, of course, contemplated. as will be clear from description given hereinabove. A

However, as will be clear from the description herein taken as a whole, a good final product is also obtained where other types of backing treatments or impregnating agents of the type hereinabove described are employed. A phenol-aldehyde type bonding coat may be employed with satisfaction with any of the impregnating coats above mentioned. Also, other bonding coats such as alkyds or modified alkyds may be employed, although bonding agents containing or comprising phenol-aldehyde type resins or similar heatconvertible resins are in most cases preferred by us in the -making of abrasive articles. Likewise while the present invention is of high utility in connection with articles comprising woven fabric backings, it has utility in connection with other fibrous bodies such as paper, where the fibers are felted rather than woven, although it has very important utility in connection with woven brous material,

While the invention has been illustrated hereinabove in considerable detail in connection with the making of abrasive sheet goods, particularly such as abrasive belts, it will be understood that the invention is not to be limited by the illustrations. For example it will be recognized that a composite article of this process would have utility even though the solid particles embedded in the grit-bonding coat were not intended for abraiding operations. Furthermore it will be recognized that sheet goods can be made up in accordance with the teaching herein presented where no granules or like-hard particles. whether of a decorative or other nature, are embedded in the surface'coating, and whether or not the latter comprises a phenol-aldehyde resin or other modified or equivalent material.

Fibrous backing described herein, while ordinarily desired, particularly in abrasive articles such as abrasive belts, is usually employed primarily for the purpose of adding strength and endurance to the finished article. -Where the finished article has sufficient strength for purposes desired in the absence of the fibrous or cloth backing, it will be understood that the same may be dispensed with while still following the teaching of this invention, for example ,in regard to the matter of securing good adhesion or a good bond between a base or backingr coat or layer and a contiguous overlying sheet or binder coat. as the case may be.

While hereinabove an abrasive article has been discussedfcomprlsing a fibrous backing material, an impregnating or backing coat therefor, a presize coat, a back-size coat, a grit-bonding or binder coat adapted to be applied over the presize coat, a layer of granules or abrasive particles or the like embedded in said binding coat and a sandsize or abrasive-size coat over the layer of granules or particles, yet nevertheless it will be understood that this invention is by no means limited to such a specific illustration and comprehends composite articles comprising a plurality of layers of material joined together in accordance with the teaching of this invention whether they have such a number or variety of layers or coatings, or not. For example the backsize coat, the presize coat, and/or the sandsize coat might be absent, while still making aI cornposite article comprising an impregnated fibrous backing to which a grid binder coat was joined in integral or contiguous relation. These and other variations within the scope of the appended claims are contemplated.

While hereinabove we have described the coat which intervenes between the relatively hard grit bonding or binder coat and the backing as being made up primarily of one of various particularly named materials, including vinyl acetal resins, cellulose derivatives such as ethyl cellulose and ethers of cellulose, olefine-polysulfide type resins and substituted butadiene polymers, all of which are organic, thermoplastic synthetic resinous materials, it will also be understood that we may employ a mixture of these ingredients as the impregnating coat or presizing coat, which intervenes between the relatively hard grit binder coat and the sheeted or woven or fibrous backingl Having thus described our invention and illustrated its use, what we claim as new and desire to secure by Letters Patent is:

1. A exible abrasive article oi the coated abrasive type adapted to be used wet in the abrading or polishing of glass, marble and the like which comprises a sheet backing material, an impregnating or sizing coat for said sheet material which consists of a film-forming, waterprooi'yadhesiv material comprising a. substantially nonoxidiz i?,

able thermoplastic synthetic resin from the group consisting of polyvinyl acetals, substituted butadiene polymers of thermoplasticcharacter, and thermoplastic adhesive cellulose derivatives; a water-resistant synthetic grit vbonding or binder coat overlying said impregnating or sizing coat,

and joined to the impregnated' brous backing aforesaid; and a multiplicity of abrasive particles embedded in said grid bonding coat; said grit bonding coat being less exible and very substantiallyv harder than said impregnating or sizing coat.

2. A flexible abrasive article comprising a sheet of fibrous material and at least two layers or coatings of material, all Joined in integral relation, one oi said coatings being an abrasivebonding coat and another of said coatings intervening, at least to substantial extent, between said abrasive-bonding coat and said fibrous material and being composed of asubstance comprising a cellulosic derivative of the group consisting of thermoplastic esters and ethers of cellulose, said abrasive-bonding coat comprising a heat-convertible synthetic resin, and a layer of abrasive grits 'embedded in said abrasive-bonding coat.

3. A exible abrasive article comprising a sheet of fibrous material and at least two layers or coatings of material, all joined in integral relation, one of said coatings being an abrasive-bonding or binder coat comprising a heat-convertible phenolic resin and another of said coatings intervening to substantial extent between said abrasive-bonding coat and said brous material and being composed of a substance comprising a cellulosic derivative from the group consisting of thermoplastic esters and ethers of cellulose, and a multiplicity of abrasive particles embedded in said binder coat.

4. A exible abrasive article comprising a sheet of strong iibrous material and at least two layers or coatings of material, all joined in integral relation, one of said coatings being an abrasivebonding coat and another of said coatings intervening to substantial extent between' said abrasive-bonding coat and said fibrous material and being composed of a substance comprising an ethyl cellulose, said abrasive-bonding coat comprising a heat-convertible synthetic resin, and a layer of abrasive grits embedded ln said abrasivebonding coat.

5. A iiexible abrasive article comprising a strong sheet of woven fibrous material and at least two layers or coatings of material, all joined'in integral relation, one of said coatings being- .an abrasive-bonding or binder coat comprising a -heat-convertible phenolic resin and another of said coatings intervening to substantial extent between said abrasive-bonding coat and said iibrous material and being composed of a substance comprising ethyl cellulose, and a multiplicity of abrasive particles embedded in. said binder coat.

6. A flexible water-proof abrasive article comprising a sheet of strong, woven brous material and at least two layers or coatings of different materials, all joined in integral relation, one of said coatings being an abrasive-bonding coat and another of said coatings impregnatingsaid brous backing material and intervening to substantial extent between said abrasive bonding coat and said i-lbrous material and being composed of a substance comprising .an ethyl cellulose, said abrasive-bonding coat comprising a phenolic-aldehyde resin and having a multiplicity or layer of abrasive grits embedded therein. Y

'7. A flexible abrasive article comprising a sheet of ilbrous material and at least two layers or coatings of material, all joined in integral relation, one of said coatings being an abrasivebonding coat and another of said coatings intervening between said abrasive-bonding coat and said :dbrous material and being composed of a substance comprising a substituted butadiene polymer which is thermoplastic and isvoi.' a solid, rubbery nature under ordinary temperatures, said abrasive-bonding coat comprising a heat-convertible synthetic resin, and a layer of abrasive grits embedded in said abrasive-bonding coat.

8. A flexible abrasive article comprising a nexible backing and at least two layers or coatings of material, all Joined in integral relation, one of said coatings being an abrasive-bonding or binder coat comprising a heat-convertible phenolic resin and another ci' said coatings intervening to substantial extent between said abrasive-bonding coat and said exible backing and being composed of a substance comprising a substituted butadient polymer'which is thermoplastic and is of a solid, rubbery nature under ordinary temperatures, and a multiplicity of abrasive particles embedded in said binder coat.

9. A flexible water-proof abrasive article cornprising a sheet of wcven fibrous material and at least two layers or coatings of material all Joined in integral relation, one of said coatings being an abrasive-bonding coat and another of said coatings intervening to substantial extent between said abrasive-bonding coat and said brous material and being composed oi a substance from the group consisting of anios-butadiene and dimethyl-butadiene and mixtures thereof, said abrasive bonding coat comprising a phenolic-aldehyde resin and having a multiplicity or coating of abrasive grits embedded therein.

10. A ilexible abrasive article comprising a sheet of brous material and at least two layers or coatings of material, all joined in integral .relation, one of said coatings being an abrasive-bonding coat and another of said coatings intervening to substantial extent between said abrasive-bonding coat and said fibrous material and being composed of a substance comprising a vinyl acetalv resin, said abrasive-bonding coat comprising a heat-convertible synthetic resin, and a layer of abrasive grits embedded in said grit-bonding coat.

1l. A exible abrasive article adapted to be used wet for abradingjor polishing glass, marble and the like which comprises a fibrous sheeted backing; and impregnating or sizing coat for said backing which consists of a nlm-forming, waterproof adhesive material comprising a vinyl acotal resin; a dissimilar synthetic grit bonding or binder coat overlying said sizing coat and joined in integral relation therewith, said grit bonding or binder coat being less flexible and very substantially harder than said impregnating or sizing coat, and having a hardness at least substantially as great as that of a straight phenol-formaldehyde resin; and a multiplicity oi abrasive particles embedded in said grit bonding coat.

12. A exible abrasive article adapted for use in the Wet sanding of glass comprising astrong brous sheet and at least two layers or coatings of material, all joined in integral relation,4 one of said coatings being an abrasive-bonding or binder coat comprising a heat-convertible phenolic resin and another of said coatings intervening to a substantial extent between said bonding coat and said brous sheet and comprising a vinyl acetal resin, and a layer of abrasive grits embeded in said binder coat.

13. Al flexible abrasive article adapted to be used wet for abrading or polishing glass comprising a fibrous base and a plurality of coatings of organic material .over said fibrous base, one coating consisting o1 a film-forming, waterproof adhesive material comprising a mixture of a polymeric vinyl acetal, a substituted butadiene polymer of plastic nature and a thermoplastic adhesive cellulose derivative from the class consisting oi' ethers and esters of cellulose; a second coating being an adhesive bonding or binder coat and being harder and less extensible than the first-mentioned coating and comprising a heatconvertible synthetic resinous material, and a layer ot abrasive grits embedded in said gritbonding coat; the mst-mentioned coating preventing any substantial penetration of the lastmentioncd coating into said brous base.

14. A ilexible abrasive article comprising a sheet of fibrous material and at least two layers or coatings of material, all joined in integral relation, oneV of said coatings being an abrasivebonding coat and another of said coatings intervening to substantial extent between said abrasive-bonding coat and said nbrousmaterial and being composed of a substance comprising a methacrylate resin, said abrasive-bonding coat comprising a heat-convertible synthetic resin, and

a. layer of abrasive grits embedded in said grit- JOSEPH H. KUGLER. BYRON J OAKES. 

